Tie-layer adhesives are used to bond polyolefins to dissimilar substrates in multilayer, co-extruded structures, particularly for blown and cast film, extrusion coating, blow molding, sheet extrusion, wire & cable, pipe, and other industrial applications. The tie-layer adhesive typically comprises a polyolefin base resin, which is the predominant component, and a grafted polyolefin. The grafted polyolefin is produced by reacting a polyolefin with an unsaturated monomer at elevated temperatures with or without a free-radical initiator. Commercially available tie-layer adhesives include Plexar® resins, product of Equistar Chemicals, LP, which are anhydride-modified polyolefins.
Polyethylene (PE) resin layers are often included in multi-layer structures having tie-layer adhesives. Liner low density polyethylene (LLDPE) is one of the most widely used polyolefin base resin. Ethylene-vinyl alcohol (EVOH) copolymers and polyamides are also widely used as oxygen barrier layers in polymeric multi-layer structures used in food packaging applications.
Grafted polyolefins are also known to be used in tie layers. For example, U.S. Pat. Appl. Publ. No. 2010/0174036 teaches that tie-layer adhesives useful for multilayer films having a favorable balance of clarity and adhesion can be made by blending, in sequence, a grafted (“maleated”) polyolefin, a polyolefin elastomer, and LLDPE.
Also known are polyolefins made from hybrid catalysts. For example, WO 2009/103516 discloses the preparation of polyethylene homopolymers and copolymers using two different single site polymerization catalysts, one of which A) is a metallocene polymerization catalyst and of which B) is a catalyst based on a transition metal complex.
A wide variety of formulations have been used to make tie-layer adhesives. The present application is directed to improved systems, methods and compositions for production of tie-layer adhesives.